Ultrasonic nebulizers are widely used for the inhalation of medications, nebulization of liquid fuel, moisturisation of air and for other uses.
A typical device for the nebulization and transport of aerosol which is used in ultrasonic nebulizers is described on p.298 of "Utrasound" (in Russian) in the series "Small Encyclopedia", published by "Soviet Encyclopedia" Publishing House, Moscow 1979.
The disadvantage of this device is the return of a large proportion of non-nebulized liquid reflected from the fountain shield back to the liquid being nebulized in the area of the active part of the fountain (i.e. the base), where the intensity of the ultrasound is maximized. This results in both a higher load on the ultrasonic transducer as well as increased waviness of the liquid being nebulized, thus defocusing transmitted energy. Both of these factors reduce effectiveness and stability of nebulization.
It is known that drops of liquid (and particles of aerosol) returning to the container have a higher temperature than the liquid that is being nebulized because of the work necessary for their creation through which they have absorbed added energy. Where these drops return to the liquid being nebulized, the temperature of the liquid changes according to random law. This further destabilises the acoustic characteristics of the medium, intensifying defocusing and lowering efficiency and stability of nebulization.
The other disadvantage of this device is the need of a separate fan for transporting the aerosol to the user.
Some of the disadvantages in the above-mentioned device are avoided in U.S. Pat. No. 4,410,139 issued Oct. 18, 1984. As shown in this patent to reduce the influence which the returning non-nebulized liquid has on effectiveness and stability of the nebulization, the ultrasonic transducer is placed at an angle different from ninety degrees to the axis of the nebulization chamber. On the bottom of the container of this device a slotted partition which surrounds the fountain is set up. It is positioned so that the major portion of the non-nebulized liquid falls outside the perimeter of the partition.
This device has some disadvantages, which reduce its efficiency and complicate its construction. The main disadvantages are:
1. The necessity to put an ultrasonic transducer at an angle to the surface of the liquid being nebulized, which leads to the significant complications in the construction of its mounting in the container holding the liquid being nebulized and therefore increases the dimensions of the said container.. PA0 2. Asymmetry of the nebulization process caused by the axis of the fountain being positioned at an angle to the axis of the container, thus leading to: PA0 3. Additional losses caused by dissipation on the partition of the energy of the ultrasonic wave which passes through the liquid being nebulized. PA0 4. A need for a fan to effect aerosol transport.
a) Increase in waviness of the liquid which then increases defocusing of transmitted energy.
b) Reduction of nebulization efficiency at low levels of liquid, caused by the liquid's surface being non-perpendicular to the direction of propagation of the ultrasonic wave front.
In summary, even though the outlined device allows certain improvement in the efficiency of nebulization, its disadvantages mentioned above restrict substantially its effectiveness.
The object of this invention is the creation of an improved device for nebulization of liquid and transport of aerosol assuring higher efficiency and stability as well as greater uniformity of the aerosol particles and delivery of the aerosol to the user without the need of an added fan; this is to be provided by means of diverting the major portion of the recycled non-nebulized liquid to the area of the container remote from the base of the fountain and the establishment (for transport of the aerosol) of a differential air pressure by reducing the cross-section of a part of the channel along which the stream of the fountain moves (Bernoulli's Law).
This object is achieved by means of designing the nebulization chamber in two parts: the expansion chamber including a bottom in which one incorporates outlet(s), as well as an intake tube inserted in the bottom of the expansion chamber and located above the base of the fountain stream of liquid being nebulized; the system of transport of the aerosol to the user is accomplished in the form of the above mentioned intake tube, and inlet(s) located on any section of the nebulizer with/without a supplementary tube(s) connected to the inlet(s) and passing through any section of the nebulizer in order for the outside air to enter by means of free (unforced) flow into the intake tube from the side of the container holding the liquid being nebulized.